sitting duck

1. N-COUNT If you say that someone is a sitting duck, you mean that they are easy to attack, cheat, or take advantage of. 易受攻击的目标; 容易受骗的人; 容易被人利用者[非正式]

Nancy knew she'd be a sitting duck when she raised the trap door. 南希知道，当她抬起陷阱门时，她就会成为被攻击的目标。